In our previous post, “More Concerning News Regarding Flea and Tick Products for Companion Dogs and Cats”, we discussed the evidence that fluralaner – one of several formulas in the isoxazoline class that is the active ingredient in Bravetco® chewables – accumulates in the fat of companion dogs and cats.

A recent Dutch study found fluralaner; afoxolaner (NexGard®; another chewable drug in the isoxazoline class); fipronil (Frontline®; topical); and imidacloprid (Advantage® or Seresto®; topical) in the environment.

You might think the two studies are contradictory. We think they are complementary. Even though fluralaner – and presumably afoxolaner and other isoxazolines by extension – may be absorbed, it is not entirely absorbed, so the rest is expelled from the body. Think of fat-soluble vitamins. While high doses may result in toxicosis; a portion of fat-soluble vitamins are excreted in feces.

Quite frankly, we are not surprised that flea and tick products were found in the outdoor environment. For years, all of us have heard about antibiotics and antidepressants in wastewater.

However, we are surprised at the pervasiveness and transference of these products in the environment to other species and living organisms, including bird nests, for example.

We encourage you to read the study. We also point out a couple of items that might put their study in context.

Bear in mind, that this is a relatively small study survey and included just nine companion dogs. Eight of them had been treated with some sort of flea and tick product.

English Springer Spaniel – Fluralaner
German Longhaired Pointer – Dinotefuran/Pyriproxyfen/Permethrin
Sprocker Spaniel – Sarolaner (isoxazoline)
Jack Russell Terrier – Sarolaner
Dutch Smoushond – Fluralaner
Old German Herding Dog – Imidacloprid/Flumethrine
Short Haired Dachshund – Sarolaner
Border Collie/Australian Shepherd Mix – Sarolaner
English Cocker Spaniel – Not treated by companion pet parent, but had been in a boarding kennel for one week before sample was retrieved

Hair Results

All nine dogs provided hair samples. Seven out of the nine had detectable levels of fluralaner in their hair, but only two had been treated with it. All nine dogs had fipronil detected in their hair, but none had been treated with it. Additionally, all nine had imidacloprid detected in their hair samples, yet only one had been treated with it. Afoxolaner was not detected in any hair samples, but five out of six dogs had detectable levels of it in their urine. None of the dogs had been treated with afoxolaner.

How is this transference occurring? The easiest explanation is mingling with other dogs or co-habiting with companion cats. One of the limitations we found is that we do not know the activity levels of these dogs except that one stayed in a boarding facility. For instance, do they visit dog parks regularly?

The researchers did touch on food. In Europe, these four chemicals have a limited use beyond flea and tick control treatment products, so food was dismissed as a potential contributing source. However, we have other thoughts…keep reading…

Water

Three of the dogs participated in a swimming experiment to determine how much water could be contaminated with the chemicals. Each dog swam separately, but the water was not changed between dogs. We would have preferred a larger sample size and hoped that the unchanged water would include a comparative control. However, the team did discuss other studies that discovered levels of fipronil and imidacloprid in wastewater and surface water. Fluralaner and afoxolaner are newer drugs on the market, so the researchers could not find any wastewater studies involving them.

Bird’s Nest

Birds not only use twigs, but also hair to manufacture their nests. The researchers tested one nest and found detectable levels of fipronil, fluralaner, and imidacloprid in the nest. This was not some random “grab an item from nature and test it”. A previous study demonstrated fipronil, imidacloprid, and fluralaner in dead juvenile birds, and hypothesized that the mortality was linked to these chemicals.

In many areas of the world, fluralaner is allowed to be used (Exzolt®) to treat poultry mites or infestations in poultry populations. Typically, it is added to a flock’s drinking water.

This makes us wonder whether the researchers dismissed food transfer sources too quickly. They did not test the food of the study dogs, but did discuss another study that looked into imidacloprid. That study found that imidacloprid was not detected in a controlled dog food diet, yet imidacloprid was detected in urine of untreated dogs. However, we think this area of research – ‘up transfer’ of chemicals in the food chain – deserves more exploration. Indeed, we already know about the persistence of PFAS in the environment, mercury in fish, and nitrates and nitrites in pet food.